64% of online gamers are female

The survey defined active gamers as those who are 13 years or older, own at least one game device, and play at least one hour of video games a week. Game devices include game consoles, personal computers and handhelds. Nielsen surveyed 2,200 active gamers online in July.

"The expansion of next-generation hardware and technology in the marketplace is simultaneously delivering new ecosystems of social exchange, interactive entertainment, media experiences and advertising models," Emily Della Maggiora, a senior vice president of Nielsen Interactive Entertainment, said in a statement.

The survey found that while the casual game segment is growing, casual gamers tend to jump from one free demo to another with little sense of brand loyalty. While banner advertising provides a good revenue stream for the online game providers, gaining brand loyalty and getting people to spend money for subscriptions or downloads will be the key to growing the market, Nielsen researchers found.